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Jun 15, 2011 (Vol. 31, No. 12)

Dispensing with Manual Pipetting

Automated Systems Trump the More Labor-Intensive Methods in Almost Every Situation

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    Tecan scientists are using Artel’s MVS Multichannel Verification System to confirm that Freedom EVO liquid-handling systems perform to specifications.

    Laboratories performing a diverse range of applications, including sample preparation for next-gen sequencing, high throughput, low-volume compound screening or PCR reactions, enzyme-based assays, or maintenance and storage of large compound or cell collections, for example, are looking to automate processes previously done manually and, in particular, liquid transfer and dispensing.

    When faced with the many automated liquid-handling systems and robotic platforms available today, labs need to consider the range of protocols they might like to automate to meet not only their current but also their future needs. They can then compare the breadth of automation capabilities and the potential flexibility of the different commercial instruments to find the best match and, ideally, avoid having to purchase multiple instruments over time, each dedicated to a particular application and not amenable to broader-scale integration into the lab’s overall workflow.

    A variety of automated liquid-handling solutions are available. Their range of features and capabilities vary as do the types of applications for which they are most suitable and beneficial.

    The service group at Tecan uses Artel’s MVS® Multichannel Verification System to confirm that Freedom EVO liquid-handling systems are performing to manufacturer’s specification for installations or following maintenance on an existing system.

    MVS uses standardized reagents that are dispensed by the liquid handler being evaluated, and the volume of liquid in each well is measured using a dual-dye, dual-wavelength ratiometric method. When dispensing into a 96-well microplate the MVS specification for inaccuracy is less than 3% and less than 1.5% for imprecision, and less than 10% and less than 3%, respectively, for a 384-well plate.

    Using the components of the MVS ensures that true volume performance is being measured, explains Debbie Bowers, director of sales for liquid-handling robotics at Tecan. “The Artel technology allows laboratories to compare standardized results across labs, whether in the same building, state, or country.”

    The partners report better results for a PCR assay performed using a manual protocol that called for the transfer of a 15 µL volume of liquid than for the same assay performed with an automated liquid-handling instrument. Whereas, the initial assumption was that the problem was with the robot, application of the Artel method showed that the manual pipettor was actually dispensing 15.67 µL of liquid. When the robot was programmed to dispense 15.67 µL, the results of the PCR assay performed using the two methods were similar.

    The overriding message, emphasizes Bowers, is that selection, utilization, and validation of an automated liquid-handling system should be matched to the user’s specific needs and applications. When comparing liquid handlers, the overall specifications of an instrument should be secondary to the specifications that are relevant to a particular application.

    “Tailor the features of a pipetting channel to the application needs,” Bowen says, taking into consideration, for example, liquid volumes, properties of the liquids to be dispensed, types and sizes of tips, plates, and tubing to be used, and the specific protocols to be automated.

    With this in mind, she feels that flexibility and scalability are key advantages of the Freedom EVO systems, with their selection of 2- to 16-channel liquid-handling arms or the MultiChannel Arm™ 96 or 384 dispensing heads and the ability to transfer liquid volumes ranging from 100 nL to 5 mL, which can be extended to upwards of 50 mL with the DynamicFill™ Technology. Additional features include liquid-level sensing during pipetting and the Pressure Monitored Pipetting (PMP™) option, which detects pipetting errors by comparing recorded and real-time-simulated pipetting pressure signals.

    According to TTP LabTech, its mosquito® HTS nanoliter liquid handler is useful for performing serial dilutions and plate replication and reformatting. For low-volume serial dilutions and sample transfer to assay-ready plates, the capability to pipette volumes from 1.2 µL down to 25 nL makes it possible to go directly from a 96-well to a 1,536-well plate format.

    A recent case study presented customer data from an 11-point serial dilution that compared manual pipetting to automated pipetting of samples in DMSO. The two methods yielded virtually identical levels of a fluorescent label at each dilution point, demonstrating at least equivalent automated pipetting accuracy.

    Joby Jenkins, product manager for the mosquito, attributes the liquid handler’s accuracy to two main features of the technology: positive displacement-based liquid transfer and precise Z positioning. With positive displacement, the pistons come in direct contact with the liquid in the pipette tip, pushing the liquid out of the tip. This allows for high-accuracy, low-volume pipetting of liquids with a broad range of “surface tensions and viscosities with no set-up changes” or recalibration, including dispensing of plasma or cell preparations at nanoliter scale.

  • Low-Volume Pipetting

    TTP designed the mosquito with a dispensing head that moves only in a vertical plane. The head is lowered to perform contact pipetting into plates that move across the deck of the instrument. This design improves positioning accuracy and avoids errors that might be introduced when trying to align a dispensing head with a plate and using air-displacement dispensing to propel the liquid into the wells of the plate.

    He emphasizes the importance of minimal dead volume for low-volume liquid transfer applications. The <500 nL dead volume of the mosquito allows users to access virtually all of the material in the source plate. “You can use even a 1 µL mother plate volume and then stamp out to low-volume assay-ready plates.”

    In the comparative case study, the source plate was a 384-well PicoTube storage system, composed of microtubes in a 384-well plate footprint. Each microtube has an individual foil seal that must be pierced before the contents can be accessed. The 0.8 mm (external diameter), needle-like dispensing tips on the mosquito pierce the foil seals as the liquid is transferred, without the need for a separate piercing step.

    TTP is developing a larger-volume pipette tip for the mosquito, with a dispensing range of 500 nL to 5 µL, and plans to launch the mosquito HV (high volume) later this year.

    Manual pipetting is a practice so commonplace in laboratories that handing the task over to an automated instrument may require a real leap of faith. Thermo Fisher Scientific hopes to make that transition a bit easier with its new automated pipetting system, the Versette™. The modular device is designed to be “versatile and scalable from an instrument, pricing, software, and consumables perspective,” says Kiara Biagioni, product manager, automated liquid-handling equipment.

    It targets a variety of automated liquid-handling applications including serial dilutions, cherry-picking, plate replication, assay development, compound library screening, and genomics.

    Users can start with a single-channel pipetting head and a two-position stage configuration and add on to the instrument as their needs evolve, selecting from 19 interchangeable pipetting heads with 1 to 384 channels, air-displacement disposable tip or a fixed-tip format dispensing technology, a dispensing range of 0.1–1,250 µL, and a two- or six-position deck. The 96- and 384-channel pipetting heads feature Thermo’s D.A.R.T.s tips, with a surface sealing design that provides consistent tip height and alignment, “which is critical for low-volume dispensing procedures.”

    Versette Clip Tips attach the tips to the single-, 8-, and 12-channel pipetting heads, with a sealing interface that prevents tips from falling off and reduces wear and tear on the instrument. All of Versette’s pipetting heads include RFID tags that identify and track usage. The ControlMate software interface includes a preset library of liquid classes, such as percent DMSO, which allows the instrument to optimize accuracy for different liquid properties.

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